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Old 3rd October 2017, 03:23 PM   #1
BenBRG
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Default Fine rattle at specific (2k) rpm

Hi all

Having driven my new (to me) car I've noticed that there's a fine/high pitched rattle within a small rpm band (1900-2100rpm ish).

The car only does it when in gear (any gear) and on throttle. Revving in neutral does not cause these symptoms. It sounds like it's coming from the rear under the rear seat bench, though I know in car sound dynamics can be very misleading.

There's no associated vibrations and the engine sounds and pulls cleanly. It doesn't at first glance 'feel' serious.

I'm not familiar with the underside of the E46 - I'm guess this could be some kind of heat shield for the exhaust?

Is this a common issue for E46's?

Any suggestions as to what might causing it are gratefully received.

Thanks
Ben
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Old 3rd October 2017, 03:24 PM   #2
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PS just to add that I've tried searching and Googling, obviously a rattle isn't a very easy thing to narrow down so I've had very little luck in finding anything that tallies with my symptoms
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Old 3rd October 2017, 06:13 PM   #3
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Wait for the headgasket purveyors of impending doom...as your symptoms do sound similar.

However, there is a heatsheild that protects the N/S drive shaft inner CVJ which is known to detach itself from one or more of its 4 mounting points which could cause a rattle, as can cat heatsheilds, and the main exhaust heatsheild above the prop. Best to get it up in the air and have a poke around.
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Old 3rd October 2017, 07:05 PM   #4
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Quote:
Originally Posted by TrojanHP View Post
Wait for the headgasket purveyors of impending doom...as your symptoms do sound similar.

However, there is a heatsheild that protects the N/S drive shaft inner CVJ which is known to detach itself from one or more of its 4 mounting points which could cause a rattle, as can cat heatsheilds, and the main exhaust heatsheild above the prop. Best to get it up in the air and have a poke around.
If it was headgasket, wouldn't it manifest itself when revved in neutral?

Car is having an alignment tomorrow so I'll ask them to take a look for anything out of the ordinary.
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Old 3rd October 2017, 07:22 PM   #5
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Not that I've ever heard. It normally manifests itself under light load, going up a slight incline ect.

It could be any number of things, but best to discount the simple first in my experience.
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Old 9th October 2017, 02:10 PM   #6
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The car has been up on the ramp. Small heat shield near the rear is missing so it's definitely not that! The cat heat shield skin was tack welded in a few places to stop it vibrating against the cat. This hasn't resolved it.

Any other ideas?

It occurs under part or full throttle, any gear. Doesn't happen when revved in neutral or when the clutch is depressed. Seems to to be gone when the car starts from cold but quickly appears after a minute or two, I assume this could be to do with something heating up and expanding?
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Old 10th October 2017, 06:07 PM   #7
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Have a compression test done. Plenty on here about what results to expect. Hopefully
its not that but best to check.
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Old 10th October 2017, 10:34 PM   #8
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My head gasket went. I had a metallic 'tinking' sound (pinking) between 2-3k revs part-throttle under load, so as the guy above says, mainly manifesting itself when labouring the engine up a hill. I thought it was heat shield rattling too, although it never sounded like it was coming from the rear. It didn't do it when in neutral, only under load.

I don't think yours is head gasket to be honest as it's happening under such a small rev range (also my noise went under full throttle), sounds much more like something is resonating (although I'm no mechanic, just my opinion!). Worth doing a compression check though just to rule it out as driving around with a misfire can cause further damage.
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Old 16th October 2017, 02:37 PM   #9
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I had an engine noise at those speeds, but limited to 5th and 6th gear that I could hear it with a little load on the throttle. sounded like it was from the engine and not the rear at all. A vanos rebuild sorted it, with the rattle repair parts and re drilled oil pump disc.

Make sure all those heat shields are checked!

There are small screws fixing various parts of the heat shields that can fail. Well, the heat shield corrodes and breaks around the screw. This leaves it free to rattle more. I re affixed mine with some large Volkswagen heat shield retainer washers over the OE screws, holding a larger un damaged area of the heat shield.

takes a bit of time under the car to go round the shields for a good look and a gentle prod to see what is loose. you'll need a friendly mechanic that isn't rushing to get it checked well....
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